Eichener See, Periodic karst lake near Eichen, Germany

The Eichener See is a temporary inland lake in a doline depression near Schopfheim, formed by groundwater emergence. The basin is surrounded by gentle slopes and shows varying water depths depending on the season.

The lake was first scientifically documented in 1782 by Heinrich Sander, sparking academic interest in the site. Its nature as a temporary lake that appears and disappears based on groundwater levels makes it a remarkable phenomenon of local geology.

Locals call it Eiemer See in Alemannic dialect. A legend tells of a farmer who promised his youngest daughter to the underground lake spirits if they watered his fields; when she tried to flee with her lover, the waters rose and drowned them. When the lake reappears, farmers say the spirits are recalling that betrayal.

The area is accessible by bus line 7335 from Schopfheim, heading toward Wehr or Bad Säckingen. Visitors should note that depending on the season and groundwater levels, the lake may be dry or filled with water, so checking conditions beforehand is wise.

The lake bed is the only confirmed German habitat of the fairy shrimp Tanymastix lacunae; only seven other confirmed sites are known in all of Europe. Its life cycle requires the basin to dry out completely, so the shrimp depend on the lake's periodic disappearance.